Certain very stringent performance requirements must be imposed on a crew escape device such as an ejection seat system, for example, to insure the device will operate successfully when ejecting a pilot or crew member from the craft which carries the device. These requirements become particularly stringent in certain kinds of ejection situations where the craft is sinking, and where the craft is already at a low altitude above the ground and/or the craft is in a nonoptimal orientation for ejection. For example, a situation of this kind is ejection from an airplane when the airplane is flying upside down and sinking at a very low altitude.
To safely eject in this type of situation, the escape device must meet the following key performance requirements: First, during ejection it is important the device shall not hit any structural part of the craft which carries the device, such as an airplane's vertical tail section, for example. Second, the altitude required to permit the device to be catapulted or separated from the craft, and to permit the device's propulsion system to re-orient the device, and to gain altitude as may be necessary so that a recovery parachute can be deployed and a successful ejection made, must be minimized. In this regard, for immediate life threatening situations, the altitude required must be minimized by maximizing vertical acceleration and attitude rates within the constraints of allowable acceleration and attitude rates which can be sustained by a pilot or crew member without serious injury. On the other hand, if minimum altitude required for safe ejection is unimportant, as in a high altitude ejection, for example, then acceleration and attitude rates can and should be minimized to keep the probability of pilot or crew member injury low.
Lastly, and in keeping with the desire to control acceleration and attitude rate limits, it is also important to stabilize the device. This means stabilization in all of three possible axes of direction, and includes control to within a desired range of both the device's side slip angle and angle of attack relative to the wind. This last requirement becomes especially important at high speed conditions for those escape devices which are in the form of open ejection seats where the effectiveness of pilot or crew member wind-blast protection devices, which are normally connected to such seats, depends heavily on wind orientation.
The capabilities of current escape devices have not kept pace with the expanding performance envelopes of certain kinds of craft. For example, current and future high performance aircraft have evolved to the point where the criteria they impose for safe ejection have exceeded the capabilities of current state of the art escape devices. For such aircraft, current escape devices provide inadequate stability, fixed performance levels, and no provisions for trajectory modification after ejection, and therefore cannot adjust for certain conditions which prevail at the time ejection is initiated. The invention disclosed herein meets these inadequacies and is particularly adaptable for use in connection with the needs of high performance aircraft, spacecraft or aerospace planes.